SITE INFORMATION AND CORRESPONDENCE

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Mr. Marshall Cloud August 31, 2004 Page 3 of Significant Differences (ESD) in section 2.0 and include: reference in the Installation Master Plan for land use changes or construction activities, notification procedures for regulatory agencies, annual review and maintenance of the controls, notification of regulatory agencies of any deficiencies in the controls, and following defined United States Army procedures for a change in land use. Existing LUCs, future industrial use of the site, and ongoing ground water monitoring, will ensure the long-term effectiveness of the remedy and will protect human health and environment well into the future. SWMU 20 SWMU 20 is the location of a former 500-gallon aboveground storage tank (AST) which contained waste solvents from Building 10. This AST was removed prior to April 1992. The SWMU 20 site also included a 2,000 gallon underground storage tank (UST) #13, containing No. 2 fuel oil and was removed in 1987. The UST site is being regulated under the Tri-Regional Guidance by the Regional Water Quality Control Board. The remedial actions at SWMU 20 included soil excavation and confirmation sampling completed in two phases. The first phase occurred in 1998 when approximately 27 cubic yards of soil was removed around existing maintenance sumps and manhole cover. The soil confirmation samples showed concentrations of TPH-d, dieldrin, trichloroethene and ethylbenzene that exceeded the ROD cleanup standards. In June 1999, a second phase of excavation took place at SWMU 20 when an additional 305 cubic yards were excavated, resulting in a total of 332 cubic yards removed from SWMU 20. The total soil excavated exceeded the ROD estimate of 10 cubic yards. Confirmation samples taken with Cone Penetrometer®Testing (CPT) samples taken at 14 feet bgs on the southern boundary of the excavation showed residual concentrations of TPH-d at 48 mg/kg, thus exceeding the ROD cleanup level of 10 mg/kg. DI tests determined that the remaining TPH-d was not a threat to the ground water quality goals. Residual TCE contamination currently exists directly beneath Building 10 due to the consistent detections of TCE in Extraction Well EW-011 at levels ranging from 1.3 pg/L during third quarter 2002 and 3.2 pg/L in third quarter 2003. Fortunately, three monitoring wells both down gradient and cross gradient from the site, have shown non- detects for TCE during the same reporting period. Additional fieldwork for SWMU 20 was conducted by the URS Corporation on April 12, 2004. The fieldwork involved an additional two CPT punches at discrete depth intervals both adjacent to the former UST excavation area and previous soil borings conducted during the RI. The 2004 fieldwork